A. E. Feiring, Journal of Fluorine Chemistry, 13, 7-18 (1979) discloses the use of tantalum pentafluoride as a catalyst for the addition of hydrogen fluoride to tetra- and trichloroethene and related compounds. The catalyst is also useful in fluorine-chlorine exchange reactions.
The use of tantalum pentafluoride as a catalyst for the addition of hydrogen fluoride to unsaturated compounds has been disclosed and claimed in Feiring, U.S. Pat. No. 4,258,225.
The need to provide economically attractive processes to convert certain halocarbon starting materials to highly fluorinated, hydrogen-containing alkanes useful as alternatives to current products for refrigerants, blowing agents, etc. has sparked interest in this area. The use of TaF.sub.5 or NbF.sub.5 under the conditions taught by Feiring, specifically as set forth in Column 1, Lines 62 to 63 of U.S. Pat. No. 4,258,225, requires "1 to 8 molar equivalents of HF and in the presence of 0.01 to 0.25 molar equivalents of TaF.sub.5 or NbF.sub.5 to produce a fluorinated alkane." These conditions are advantageous for addition of HF to the olefinic bonds of the starting halogenated alkenes, but are far less favorable to halogen exchange on the resulting adducts. Consequently, while highly fluorinated alkanes can be produced, the yields are too small for economically attractive production. In accordance with this invention it has been discovered that utilizing a combination of high specific catalyst loading plus a high ratio of catalyst and HF to halocarbon starting material enables the direct preparation of many highly fluorinated alkanes in economically attractive yields.
It is a particular object of this invention to provide a liquid-phase process for the preparation of 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) in high yields and with a low content of other isomers. Another object is to provide such a high yield, high purity CF.sub.3 CHCl.sub.2 process which enables the use of relatively low HF concentrations, thereby minimizing HF-induced reactor corrosion and the need for high cost, high pressure equipment.
HCFC-123 is an environmentally-acceptable alternate to trichlorofluoromethane (CFC-11) as a blowing agent, solvent, tobacco puffing agent and refrigerant. HCFC-123 is also a useful raw material for preparing 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) and pentafluoroethane (HFC-125) which are environmentally-acceptable products. HCFC-124 is useful as a blowing agent, sterilant carrier gas, propellant, refrigerant and raw material for preparing 1,1,1,2-tetrafluoroethane (HFC-l34a) --a zero-ozone-depletion-potential replacement for dichlorodifluoromethane (CFC-.sub.12) as a refrigerant. HFC-125 is a zero-ozone-depletion-potential replacement for R-502 [an azeotropic blend of chlorodifluoromethane (HCFC-22) and chloropentafluoroethane (CFC-115)]. HFC-125 is also a useful raw material for preparing tetrafluoroethylene (TFE) and a long-term candidate replacement for HCFC-22.